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Aldol Additions of Titanium and Boron Enolates of Achiral and Chiral δ‐Lactones to Achiral Model Aldehydes: Simple and Induced Diastereoselectivities
Author(s) -
Weber Fabian,
Becker Fabian,
Keller Manfred,
Hillebrecht Harald,
Brückner Reinhard
Publication year - 2015
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201501128
Subject(s) - chemistry , lactone , aldol reaction , isobutyraldehyde , aldol condensation , steric effects , boron , adduct , lactol , crotonaldehyde , stereochemistry , organic chemistry , medicinal chemistry , catalysis
We studied the steric course of aldol additions of CpTiCl 2 (novel) or Bu 2 B enolates of the unsubstituted δ‐lactone and of the four monomethylated δ‐lactones to isobutyraldehyde, crotonaldehyde, and para ‐bromobenzaldehyde. The titanium enolates reacted syn ‐selectively with >95:5 ds in most cases. The boron enolates reacted anti ‐selectively without exception ( ds = 98:2 to 92:8). These selectivities paired with a preferred trans ‐orientation of the α‐hydroxyalkyl substituents relative to the lactone's β‐ or γ‐methyl group and with a preferred cis ‐orientation relative to the lactone's δ‐methyl group. Our preparation of γ‐methyl‐δ‐lactone ( 20 ) features a tandem glycol cleavage/lactol → lactone conversion with cat. TEMPO/stoichiom. PhI(OAc) 2 , which we believe is novel.